Source Code Cross Referenced for VariableReference.java in  » XML » saxonb » net » sf » saxon » expr » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » XML » saxonb » net.sf.saxon.expr 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package net.sf.saxon.expr;
002:
003:        import net.sf.saxon.om.*;
004:        import net.sf.saxon.trans.XPathException;
005:        import net.sf.saxon.type.AnyItemType;
006:        import net.sf.saxon.type.ItemType;
007:        import net.sf.saxon.type.TypeHierarchy;
008:        import net.sf.saxon.value.SequenceType;
009:        import net.sf.saxon.value.Value;
010:        import net.sf.saxon.value.SingletonNode;
011:
012:        import java.io.PrintStream;
013:
014:        /**
015:         * Variable reference: a reference to a variable. This may be an XSLT-defined variable, a range
016:         * variable defined within the XPath expression, or a variable defined in some other static context.
017:         */
018:
019:        public class VariableReference extends ComputedExpression implements 
020:                BindingReference {
021:
022:            Binding binding = null; // This will be null until fixup() is called; it will also be null
023:            // if the variable reference has been inlined
024:            SequenceType staticType = null;
025:            Value constantValue = null;
026:            transient String displayName = null;
027:
028:            /**
029:             * Constructor
030:             * @param declaration the variable declaration to which this variable refers
031:             */
032:
033:            public VariableReference(VariableDeclaration declaration) {
034:
035:                // Register this variable reference with the variable declaration. When the variable declaration
036:                // is compiled, the declaration will call the fixup() method of the variable reference. Note
037:                // that the object does not retain a pointer to the variable declaration, which would cause the
038:                // stylesheet to be locked in memory.
039:
040:                // System.err.println("Register reference " + this + " with declaration " + declaration + " name=" + declaration.getVariableName());
041:                declaration.registerReference(this );
042:                displayName = declaration.getVariableName();
043:            }
044:
045:            /**
046:             * Simplify the expression. Does nothing.
047:             */
048:
049:            public Expression simplify(StaticContext env) {
050:                return this ;
051:            }
052:
053:            /**
054:             * Set static type. This is a callback from the variable declaration object. As well
055:             * as supplying the static type, it may also supply a compile-time value for the variable.
056:             * As well as the type information, other static properties of the value are supplied:
057:             * for example, whether the value is an ordered node-set.
058:             */
059:
060:            public void setStaticType(SequenceType type, Value value,
061:                    int properties) {
062:                // System.err.println(this + " Set static type = " + type);
063:                staticType = type;
064:                constantValue = value;
065:                // Although the variable may be a context document node-set at the point it is defined,
066:                // the context at the point of use may be different, so this property cannot be transferred.
067:                staticProperties = (properties & ~StaticProperty.CONTEXT_DOCUMENT_NODESET)
068:                        | type.getCardinality() | getDependencies();
069:            }
070:
071:            /**
072:             * Type-check the expression. At this stage details of the static type must be known.
073:             * If the variable has a compile-time value, this is substituted for the variable reference
074:             */
075:
076:            public Expression typeCheck(StaticContext env,
077:                    ItemType contextItemType) throws XPathException {
078:                if (constantValue != null) {
079:                    binding = null;
080:                    return constantValue;
081:                }
082:                if (staticType == null) {
083:                    throw new IllegalStateException("Variable $" + displayName
084:                            + " has not been fixed up");
085:                } else {
086:                    return this ;
087:                }
088:            }
089:
090:            /**
091:             * Type-check the expression. At this stage details of the static type must be known.
092:             * If the variable has a compile-time value, this is substituted for the variable reference
093:             */
094:
095:            public Expression optimize(Optimizer opt, StaticContext env,
096:                    ItemType contextItemType) throws XPathException {
097:                if (constantValue != null) {
098:                    binding = null;
099:                    return constantValue;
100:                }
101:                return this ;
102:            }
103:
104:            /**
105:             * Fix up this variable reference to a Binding object, which enables the value of the variable
106:             * to be located at run-time.
107:             */
108:
109:            public void fixup(Binding binding) {
110:                // System.err.println("Binding for " + this + " is " + binding.getVariableName());
111:                this .binding = binding;
112:                resetStaticProperties();
113:            }
114:
115:            /**
116:             * Determine the data type of the expression, if possible
117:             * @return the type of the variable, if this can be determined statically;
118:             * otherwise Type.ITEM (meaning not known in advance)
119:             * @param th
120:             */
121:
122:            public ItemType getItemType(TypeHierarchy th) {
123:                if (staticType == null) {
124:                    return AnyItemType.getInstance();
125:                } else {
126:                    return staticType.getPrimaryType();
127:                }
128:            }
129:
130:            /**
131:             * Get the static cardinality
132:             */
133:
134:            public int computeCardinality() {
135:                if (staticType == null) {
136:                    return StaticProperty.ALLOWS_ZERO_OR_MORE;
137:                } else {
138:                    return staticType.getCardinality();
139:                }
140:            }
141:
142:            /**
143:             * Determine the special properties of this expression
144:             * @return {@link StaticProperty#NON_CREATIVE} (unless the variable is assignable using saxon:assign)
145:             */
146:
147:            public int computeSpecialProperties() {
148:                int p = super .computeSpecialProperties();
149:                if (binding == null || !binding.isAssignable()) {
150:                    // if the variable reference is assignable, we mustn't move it, or any expression that contains it,
151:                    // out of a loop. The way to achieve this is to treat it as a "creative" expression, because the
152:                    // optimizer recognizes such expressions and handles them with care...
153:                    p |= StaticProperty.NON_CREATIVE;
154:                }
155:                return p;
156:            }
157:
158:            /**
159:             * Test if this expression is the same as another expression.
160:             * (Note, we only compare expressions that
161:             * have the same static and dynamic context).
162:             */
163:
164:            public boolean equals(Object other) {
165:                return (other instanceof  VariableReference
166:                        && binding == ((VariableReference) other).binding && binding != null);
167:            }
168:
169:            /**
170:             * get HashCode for comparing two expressions
171:             */
172:
173:            public int hashCode() {
174:                return binding == null ? 73619830 : binding.hashCode();
175:            }
176:
177:            public int getIntrinsicDependencies() {
178:                if (binding == null || !binding.isGlobal()) {
179:                    return StaticProperty.DEPENDS_ON_LOCAL_VARIABLES;
180:                } else {
181:                    return 0;
182:                }
183:            }
184:
185:            /**
186:             * Promote this expression if possible
187:             */
188:
189:            public Expression promote(PromotionOffer offer)
190:                    throws XPathException {
191:                if (offer.action == PromotionOffer.INLINE_VARIABLE_REFERENCES) {
192:                    Expression exp = offer.accept(this );
193:                    if (exp != null) {
194:                        // Replace the variable reference with the given expression.
195:                        //binding = null;
196:                        offer.accepted = true;
197:                        return exp;
198:                    }
199:                }
200:                return this ;
201:            }
202:
203:            /**
204:             * An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
205:             * This method indicates which of these methods is provided. This implementation provides both all three methods
206:             * natively.
207:             */
208:
209:            public int getImplementationMethod() {
210:                return EVALUATE_METHOD | ITERATE_METHOD | PROCESS_METHOD;
211:            }
212:
213:            /**
214:             * Get the value of this variable in a given context.
215:             * @param c the XPathContext which contains the relevant variable bindings
216:             * @return the value of the variable, if it is defined
217:             * @throws XPathException if the variable is undefined
218:             */
219:
220:            public SequenceIterator iterate(XPathContext c)
221:                    throws XPathException {
222:                ValueRepresentation actual = evaluateVariable(c);
223:                return Value.getIterator(actual);
224:            }
225:
226:            public Item evaluateItem(XPathContext c) throws XPathException {
227:                ValueRepresentation actual = evaluateVariable(c);
228:                if (actual instanceof  Item) {
229:                    return (Item) actual;
230:                }
231:                return Value.asItem(actual, c);
232:            }
233:
234:            public void process(XPathContext c) throws XPathException {
235:                ValueRepresentation actual = evaluateVariable(c);
236:                if (actual instanceof  NodeInfo) {
237:                    actual = new SingletonNode((NodeInfo) actual);
238:                }
239:                ((Value) actual).process(c);
240:            }
241:
242:            public ValueRepresentation evaluateVariable(XPathContext c)
243:                    throws XPathException {
244:
245:                if (binding == null) {
246:                    // System.err.println("No binding for " + this);
247:                    throw new IllegalStateException("Variable $" + displayName
248:                            + " has not been fixed up");
249:                }
250:
251:                return binding.evaluateVariable(c);
252:            }
253:
254:            /**
255:             * Get the object bound to the variable
256:             */
257:
258:            public Binding getBinding() {
259:                return binding;
260:            }
261:
262:            /**
263:             * Diagnostic print of expression structure
264:             */
265:
266:            public void display(int level, NamePool pool, PrintStream out) {
267:                if (displayName != null) {
268:                    out.println(ExpressionTool.indent(level) + '$'
269:                            + displayName);
270:                } else {
271:                    out.println(ExpressionTool.indent(level)
272:                            + "$(unbound variable)");
273:                }
274:            }
275:        }
276:
277:        //
278:        // The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
279:        // you may not use this file except in compliance with the License. You may obtain a copy of the
280:        // License at http://www.mozilla.org/MPL/
281:        //
282:        // Software distributed under the License is distributed on an "AS IS" basis,
283:        // WITHOUT WARRANTY OF ANY KIND, either express or implied.
284:        // See the License for the specific language governing rights and limitations under the License.
285:        //
286:        // The Original Code is: all this file.
287:        //
288:        // The Initial Developer of the Original Code is Michael H. Kay.
289:        //
290:        // Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
291:        //
292:        // Contributor(s):
293:        // Portions marked "e.g." are from Edwin Glaser (edwin@pannenleiter.de)
294:        //
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